Invalid Date

Hi ,
I have two issues with date fields .

1- how to make a datepicker to show (today- now()) by default , I tried value : new Date() , and the browser get 'newDate' and of course is undefine , even when the design view shows the correct date .

2- the control date , has format j/m/Y , and shows the right format . But after chosing a date with the picker I get in the browser invalid proto , where and what to write the code to fix this . in order to save the model properly .